1. Field of the Invention
The present invention relates to a power steering apparatus of the vehicle-speed-responsive type for increasing a steering reactive force as the speed of a vehicle increases.
2. Description of Relevant Art
Power steering apparatus hydraulically utilize power from an engine to provide the major portion of the steering force. However, a driver experiences difficulty in driving a vehicle provided with such power steering apparatus, in that he loses the feel of a steering force proportional to a resistance of a road on which he is operating the vehicle.
To solve such problem, there have been proposed and used a variety of reactive force transmission mechanisms or hydraulic pressure reaction chamber systems. However, such reaction chamber systems produce a steering force proportional to a road resistance. Such systems permits a road resistance to be transmitted to the driver when he is turning the steering wheel while the vehicle is being stopped, which is detrimental to smooth steering operation.
An attempt to eliminate such disadvantage of the known reaction chamber systems is disclosed in U.S. Pat. No. 3,994,361, which discloses a vehicle-speed-responsive type control system for controlling a steering reactive force in response to vehicle speed, rather than road resistance only.
With the known vehicle-speed-responsive type reaction control system, the operation thereof is limited up to a predetermined vehicle speed, and pressure in a reaction chamber is not capable of following an increase in road resistance at a speed above such predetermined speed.
In overcoming the foregoing disadvantages of known apparatus, the present invention provides more accurate steering in a power steering apparatus of the vehicle-speed-responsive type.